Motor shut down

[feathering]

Hi,
I have experienced 3 instances of momentary motor shutdown during flight on my Align 470LP over the course of two flights. Each shutdown lasted only a few seconds and I had full collective control during the shutdown. The events were quick enough that I could "pick up" the heli mid air and continue flying without really noticing any other issue otherwise.

The 470l is stock (ESC RCE-BL50X and motor 470MX) but my set up is perhaps a bit unusual: 4S ungoverned . When the shutdowns occurred I wasn't doing anything fancy and current draw must have been comparatively low.

Any idea of what may be causing this? Thanks

[kenny d]

I’ve seen this quite a few times , a separate bec usually resolves it , I think it’s more to do with the power supply & the flybarrless controller
some flybarless controllers are power hungry ( I.E beastx )

[coolice]

Hey buddy.

You'll find using 4's instead if 6s, which the model/ESC combo was designed to use, is that your current draw will be higher. Thus I would guess the ESC will be running a bit warmer than normal so could have shutdown, however if you weren't doing anything fancy at this point maybe this is not the cause.
But my main focus point will be your switching BEC output from the ESC, as it will be less capable on 4's input I'm sure and so it's output current capability will be reduced when run from this lower input voltage.
Most BEC's have different power ratings depending on the voltage going into them.
So from your description, it sounds like you had a brownout for a second or two, the shutdown will remove the motor load as well (thus cooling the ESC) and normal operation should return pretty quickly as it appeared to do.
Assuming DSMX at this point it recovers quickly.

I'm not sure if the Beastx is as power hungry as some other flybarless units, but flybarless in general demands a capable power supply due to the higher amp draws associated when running more gyros constantly moving the servos.
Also model airframe design now transfers much more flight loads directly to the servos, so they pull more current to hold their position.

I'd suggest trying a 6s LiPo if you can, or fit an external BEC, so you leave the ESC to control the motor only and the seperate BEC to power your flight controls.

Ian Contessa

[Grumpy]

What flybarless controller and receiver are you using? Also in what circumstances did the events occur, just in level flight or when putting high load on the motor? Have you done a range check from all orientations around the heli?

[DaveJones]

Last time I had this type of problem it was battery/weather related. Old batteries flying and flying in the cold seemed to push them over the edge triggering a LVC shutdown on my ESC which typically recovered pretty quickly

Before that I had the same symptoms that showed up as brownouts in my vBar logs, I could simulate it on the ground with excessive stick wiggling. Eventually tracked that one down to a failing tail servo through a process of trail and error (disconnect something, wiggle, fail, repeat)

If you really do have complete control of the heli during the shutdown (and I sometimes find i'm not so sure afterwards) that would suggest to me that you didn't brown out and would point to the LVC or ESC overload especially with 4S and the higher current demands, maybe try disabling the LVC and see if the problem goes away.

[Hei1950]

If you do go to 6s which is what I am using make sure if you use the governor setting that in idle up throttle curve is set between 75% and 85%, otherwise you get what appears to be a motor shut down. I have been setting up mine today I am using same esc and had set mid point below 75%. Make double sure you are not in governor mode. Also note if you are using quick speed throttle response that will increase peak current. The fact you have control to me says it nothing to do with BEC voltage.

[barryorbik]

I think Coolice (Ian) has hit the nail on the head as one of our guys had the same issue when using a 4S to set his up. Changing to a 6S cured his but an external BEC with a higher current rating than the internal BEC in the ESC would be a good idea if you do not want to use 6S.

Barry

[Grumpy]

FWIW if you keep gearing the same then current draw is lower on 4S than on 6S. It's only if you are trying to keep the same RPM and power (by using a higher Kv motor or gearing up) that current becomes higher.

[coolice]

FWIW if you keep gearing the same then current draw is lower on 4S than on 6S. It's only if you are trying to keep the same RPM and power (by using a higher Kv motor or gearing up) that current becomes higher.

Hey buddy.

Now you know that's not right surely :-)

Same model, same setup, same gear ratio is going to pull more amps when powered by 4s than 6s pack. Thats simple electronics based on efficiency between the two voltages and their ability to drive the rotors with pitch on the blades.

At lower (4s) rpm you're going to be running more pitch to hover anyway, so this alone all combines to change the current draw.

We've all seen the 700E's running a single 6s pack instead of the usual 12s and while it works (admittedly at lower rotor rpm) the amps will be more by comparison.
I'll agree this is a much bigger voltage gap than 4's to 6s, but it's only to highlight a point.

Even a simple full pitch climb is going to pull more amps on a 4's setup than a 6s.

But I think we're coming to the conclusion that the motor control side didn't have a break in output, but the BEC maybe faltered which shut down the system.
BEC's output capabilities change with input voltage usually so it's a potential clue.

Unfortunately we'll probably never know for sure, so it's all speculation and maybe's.
Being brave and trying a 6s pack will tell the tale.

Ian Contessa

[feathering]

Thank you all for your comments!

The fbl controller is a beastx and the receiver a frsky X4R-SB.

Indeed I had control when the shutdown occurred so I originally assumed that a brown out was not the cause. Meanwhile, I can see that on 4S a BEC would be a nice addition. And perhaps it is time to go 6S... One of the reasons why I fly ungoverned is to avoid large current draw on 4S: my view is that current won't be that high as any manoeuvre that leads to an increase on blade drag will simply slow down the head. Governed may be a different story though.

Battery/weather was in fact my first thought as the first shut down happened last week with snow on the ground. But then the other events occurred a day later when temperatures started going up.

Motor load at the time of the shutdowns shouldn't have been high as they happened either half-way through a flip or on level flight. Having said this I was practising rolling rainbows right before which is quite intense given the applied cyclic to make the heli roll together with the alternating positive and negative collective to make it trace the arc.

Based on your comments I think the course of action will be to put the ESC back (I took it off to make sure everything was in place) and take the heli for a test flight. If it happens again I will buy some 6S batteries before I change any component so that I can start ruling things out.

Thank you again.

[barryorbik]

Nice explanation Ian but I think you may have got the 6s and 4s cell numbers in your first line reversed, as what we are really talking about is the power demand into the motor/servo/FBL unit etc in total Watts. The power calculation is W(Watts)= V(Voltage) x A (Amps), so if we had a demand of 500W then a 4s (14.8V) pack would have to deliver 33.8 Amps, whereas a 6s (22.2V) pack would only need to deliver 22.5A.

That is only fundamental electronics but the unknown factor is how the efficiency of the BEC and ESC change with lower input voltages and higher current demands. Most power conversion circuits are at optimum efficiency when loaded between 75% + 90% of their 'normal' rating because the losses in the circuits drive components increase at lower power demand levels, resulting in a lower power efficiency which in turn results in the internal components heating up more ultimately causing the thermal protection devices within the ESC and BEC cutting the power until the temperatures reduce back to safe levels. Operating above 90% for sustained periods may cause catastrophic failure of marginally rated output devices, often due to ineffective cooling and that is when the magic smoke happens!!

Barry

[coolice]

Nice explanation Ian but I think you may have got the 6s and 4s cell numbers in your first line reversed, as what we are really talking about is the power demand into the motor/servo/FBL unit etc in total Watts. The power calculation is W(Watts)= V(Voltage) x A (Amps), so if we had a demand of 500W then a 4s (14.8V) pack would have to deliver 33.8 Amps, whereas a 6s (22.2V) pack would only need to deliver 22.5A.

That is only fundamental electronics but the unknown factor is how the efficiency of the BEC and ESC change with lower input voltages and higher current demands. Most power conversion circuits are at optimum efficiency when loaded between 75% + 90% of their 'normal' rating because the losses in the circuits drive components increase at lower power demand levels, resulting in a lower power efficiency which in turn results in the internal components heating up more ultimately causing the thermal protection devices within the ESC and BEC cutting the power until the temperatures reduce back to safe levels. Operating above 90% for sustained periods may cause catastrophic failure of marginally rated output devices, often due to ineffective cooling and that is when the magic smoke happens!!

Barry

Hey buddy.

Doh! Yes I did get them round the wrong way, just fixed it. I'm on my phone so bouncing backwards and forwards on the small screen trying to avoid errors.

Yeah I'm wondering now what the difference in BEC efficiency will be with this ESC on the differing voltages, I've not gone looking for its specs and I'm sure they might not say, but I'm sure there is a difference.
Going by memory of other ESC's quoting different specs based on input voltage, I'm assuming this will be the same.

Will be a good test with the bigger pack, but still in the back of your mind you'll be waiting in case it happens again.

Ian Contessa

[coolice]

Thank you all for your comments!

The fbl controller is a beastx and the receiver a frsky X4R-SB.

Indeed I had control when the shutdown occurred so I originally assumed that a brown out was not the cause. Meanwhile, I can see that on 4S a BEC would be a nice addition. And perhaps it is time to go 6S... One of the reasons why I fly ungoverned is to avoid large current draw on 4S: my view is that current won't be that high as any manoeuvre that leads to an increase on blade drag will simply slow down the head. Governed may be a different story though.

Battery/weather was in fact my first thought as the first shut down happened last week with snow on the ground. But then the other events occurred a day later when temperatures started going up.

Motor load at the time of the shutdowns shouldn't have been high as they happened either half-way through a flip or on level flight. Having said this I was practising rolling rainbows right before which is quite intense given the applied cyclic to make the heli roll together with the alternating positive and negative collective to make it trace the arc.

Based on your comments I think the course of action will be to put the ESC back (I took it off to make sure everything was in place) and take the heli for a test flight. If it happens again I will buy some 6S batteries before I change any component so that I can start ruling things out.

Thank you again.

Hey buddy.

There's been some good points raised from your original post, so it'll be good to try and eliminate some one by one.

One point which was a good one is the low voltage cut off point setting, especially if your packs were quite cold and didn't hold voltage so well.
Didn't think of that myself but it's a good one. I recall similar years ago with my then Century Swift, we ended up hovering for a bit to warm the packs in cold weather before then heading off into 3D. If we didn't there wasn't any power.
Of course we know more now so stick the packs in our pockets or a warm car until needed :-)

I see your logic behind the ungoverned route, but I'm also thinking it might actually work against you a bit.
Unlike an internal combustion engine, where if you load it up its rpm will sag, an electric motor will drop rpm but then pull more current to continue rotating. So with this in mind a governed setting might be better.

Please keep us posted on what you deduce from your testing.

Might be worth checking the connection from ESC to Beastx is fine, so the supply link is good. A loose connection here can cause momentary power loss.
Also the main battery connections, the solder joints I'm thinking really, just in case they're dry joints.
Clutching at straws a bit but they've all caused problems on electric models in the past.

Ian Contessa

[Grumpy]

Hey buddy.

Now you know that's not right surely :-)

I know I'm right actually. Many on line motor specifications showing the same thing (example quoted below). The reason you use less amps is that (with nothing else changed) the RPM on 4S will be 2/3rd of the RPM on 6S. Power required to drive a rotor is to the cube of RPM. 2/3rd ^3 = 0.3.. So this means that to spin a rotor at '4S RPM' takes only approx 30% of the power of '6S RPM' (which is why low headspeed helis fly much longer). Yes, you need more pitch to hover but I'm assuming here the total maximum pitch is unchanged (i said it's assumed nothing else changes when you swap batteries).

Here's a Scorpion motor data chart. If you check the current draw with the same prop current goes UP when you increase voltage. For example when fitted with an APC 10x5E prop powered with a 4S (14.8V) battery it puls 33.48A. The exact same motor and exact same prop when powered with a 5S battery (18.8V) pulls 44.57A.. these are not my figures, it's are Scorpions official data and the same trend goes for all of their motor testing and also every other manufacturer who has published data. A heli is no different, a heli rotor is basically just a large propeller.

I'd love to debate further but if you want to please start a new thread because I dont want to de-rail this one...

[Grumpy]

FWIW the current rating of the BEC will be higher at lower input voltage (not lower as mentioned previously). This is because the at lower input voltage the BEC has less work to do in order to reduce voltage to your output voltage value (i.e. input and output are closer). You can see this trend very clearly in Castles published data here: CC BEC PRO 20A MAX OUTPUT, 12S (50.4 VOLTS) MAX INPUT SWITCHING REGULATOR

For example of the Castle BEC Pro:

2S-4S: 15A
5S-6S: 13A
7S-8S: 11A
9S-10S: 9A
11S-12S: 8A